Electophoretic display device and method for fabricating the same

ABSTRACT

An electrophoretic display device includes: a first substrate having a plurality of pixels formed in a plurality of vertical pixel rows and a plurality of horizontal pixel rows; a plurality of data lines formed at every vertical pixel row of the first substrate; a thin film transistor (TFT) formed at each pixel of the first substrate and including a source electrode, a drain electrode, an organic semiconductor layer, and a gate electrode; a passivation layer formed on the TFTs and the data lines of the first substrate and including a first contact hole exposing the drain electrode of the TFT and a second contact hole exposing the gate electrode of the TFT; a pixel electrode formed on the passivation layer at each pixel of the first substrate and connected with the drain electrode of the TFT via the first contact hole of the passivation layer; a plurality of gate lines formed on the passivation layer at every horizontal pixel row of the first substrate and connected with the gate electrode of the TFT via the second contact hole of the passivation layer; a second substrate attached to the first substrate in a facing manner; a common electrode formed on the second substrate; and an electrophoretic film formed between the first and second substrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/618,405, filed Nov. 13, 2009, which claims priority to Korean PatentApplication No. 10-2008-0117731 filed in Korea on Nov. 25, 2008, both ofwhich are hereby incorporated by reference in their entireties.

BACKGROUND

1. Field of the Invention

The present disclosuer relates to an electrophoretic display device andits fabrication method and, more particularly, to an electrophoreticdisplay device capable of minimizing a step at a protection layer andminimizing the number of masks used in a fabrication process.

2. Discussion of the Related Art

In general, an electrophoretic display device is an image displayerusing a phenomenon that when a pair of electrodes receiving voltage areput in a colloid solution, colloid particles are moved to one polarity.

The electrophoretic display device is a display device in which atransparent conductive film is coated on a base film which is thin andcan be easily bent like paper or plastic to drive electrophoreticsuspension and receives much attention as electric paper that mayreplace the conventional printing mediums such as books, newspapers, andthe like.

The general electrophoretic display device will now be described withreference to the accompanying drawings.

As shown in FIG. 1, an electrophoretic panel provided in the generalelectrophoretic display device includes a first substrate 1 on whichgate lines 4 and data lines (not shown) are formed to cross each otherto define a plurality of pixels, and a second substrate 2 disposed toface the first substrate 1.

With reference to FIG. 1, the plurality of pixels defined on the firstsubstrate 1 include a plurality of vertical pixel rows and a pluralityof horizontal pixel rows. Data lines are formed on every vertical pixelrow on the first substrate 1. A thin film transistor (TFT) 5 including asource electrode 5 a, a drain electrode 5 b, an organic semiconductorlayer 5 c, a gate insulating layer 5 d, and a gate electrode 5 e isformed at each pixel, and a pixel electrode 9 in contact with the drainelectrode 5 b of the TFT 5 is formed at each pixel.

A passivation layer 8 is formed on the data lines, the TFT 5, and thepixel electrode 9 formed on the first substrate 1. Recently, in order toprevent a pixel voltage applied to the pixel electrode 9 to drive anelectrophoretic film from weakening due to the thick passivation layer5, an open area (OA) is formed at the passivation layer 8 by removing aportion or the entirety of a region overlapping with the pixel electrode9.

The gate line 4 is formed at every horizontal pixel row on thepassivation layer 8 of the first substrate 1 and is in contact with thegate electrode 5 e of the TFT 5 via a contact hole 6 provided at thepassivation layer 9.

With reference to FIG. 1, a common electrode 10 is formed on the secondsubstrate 101, and the electrophoretic film (not shown) is formedbetween the first and second substrates 1 and 2.

Although not shown, the electrophoretic film includes a plurality ofcapsules in which electronic ink including white ink and black ink isdistributed, and the white ink and the black ink are charged with eachdifferent polarity. Namely, white ink is charged with positive electriccharges, and black ink is charged with negative electric charges, orvice versa.

A method for fabricating the general electrophoretic display devicehaving such configuration will be described as follows.

First, a first masking process is performed to form the source electrode5 a, the drain electrode 5 b and a data line (not shown) on the firstsubstrate 1 with a plurality of pixels defined thereon.

Next, a second masking process is performed to form the pixel electrode9 in contact with the drain electrode 5 b at each pixel of the firstsubstrate 1.

And then, a third masking process is performed to form the organicsemiconductor layer 5 c, the gate insulating layer 5 d, and the gateelectrode 5 e at each pixel of the first substrate 1.

Thereafter, the passivation layer 8 is formed on the data line, the TFT5, and the pixel electrode 9 of the first substrate 1.

Subsequently, a fourth masking process is performed to form the contacthole 6 exposing a portion of the gate electrode 5 e at the passivationlayer 8, and the open area (OA) is formed to expose a portion or theentirety of the pixel electrode 9.

And then, a fifth masking process is performed to form the gate line 4on the passivation layer 8. At this time, the gate line 4 is in contactwith the gate electrode 5 e via the contact hole 6 of the passivationfilm 8.

In the fabrication method, the first to third masking process includes astep of sequentially forming an element formation material layer (e.g.,a pixel electrode formation material layer) and a photosensitive film; astep of forming a photosensitive film pattern by performingphotolithography on the photosensitive film; and a step of patterningthe element formation material layer by using the photosensitive filmpattern.

The related art general electrophoretic display device as describedabove requires 5 masks in its fabrication process, which, thus, isineffective in the fabrication costs and time. Thus, an electrophoreticdisplay device having a structure of requiring the minimum number ofmasks in the fabrication process and its fabrication method arerequired.

The first substrate 1 and the plurality of elements on the firstsubstrate 1 of the general electrophoretic display device as describedabove may be applicable to a TFT array substrate of a liquid crystaldisplay (LCD) device. However, when the first substrate 1 and theplurality of elements on the first substrate 1 of the generalelectrophoretic display device are applied to the TFT array substrate ofthe LCD device, rubbing of an alignment film is not smoothly made due toa step at the open area (OA) formed at the passivation layer 8 or aregion may not be filled with liquid crystal, degrading picture quality.

BRIEF SUMMARY

An electrophoretic display device includes: a first substrate having aplurality of pixels formed in a plurality of vertical pixel rows and aplurality of horizontal pixel rows; a plurality of data lines formed atevery vertical pixel row of the first substrate; a thin film transistor(TFT) formed at each pixel of the first substrate and including a sourceelectrode, a drain electrode, an organic semiconductor layer, and a gateelectrode; a passivation layer formed on the TFTs and the data lines ofthe first substrate and including a first contact hole exposing thedrain electrode of the TFT and a second contact hole exposing the gateelectrode of the TFT; a pixel electrode formed on the passivation layerat each pixel of the first substrate and connected with the drainelectrode of the TFT via the first contact hole of the passivationlayer; a plurality of gate lines formed on the passivation layer atevery horizontal pixel row of the first substrate and connected with thegate electrode of the TFT via the second contact hole of the passivationlayer; a second substrate attached to the first substrate in a facingmanner; a common electrode formed on the second substrate; and anelectrophoretic film formed between the first and second substrates.

A method for fabricating an electrophoretic display device includes:preparing a first substrate on which a plurality of pixels are definedand formed in a plurality of horizontal pixel rows and a plurality ofvertical pixel rows; forming a data line at every vertical pixel row onthe first substrate and forming source and drain electrodes at everypixel on the first substrate; forming an organic semiconductor layer, agate insulating layer, and a gate electrode at each pixel on the firstsubstrate to form a TFT; forming a passivation layer on the data lineand on the TFT of the first substrate; forming a first contact holeexposing the drain electrode of the TFT and a second contact holeexposing the gate electrode of the TFT at the passivation layer; andforming a pixel electrode on the passivation at every pixel, the pixelelectrode being connected with the drain electrode of the TFT via thefirst contact hole, and forming a gate line on the passivation layer atevery vertical pixel row, the gate line being connected with the gateelectrode of the TFT via the second contact hole.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a general electrophoretic displaydevice;

FIG. 2 is a plan view showing an electrophoretic display deviceaccording to an exemplary embodiment of the present invention;

FIG. 3 is a sectional view taken along line I-I′ of FIG. 2, showingfirst and second substrates; and

FIGS. 4 a to 4 l are sectional views showing the sequential steps offabricating the electrophoretic display device of FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERREDEMBODIMENTS

An electrophoretic display device and its fabrication method accordingto exemplary embodiments of the present invention will now be describedin detail with reference to the accompanying drawings.

First, the configuration of the electrophoretic display device accordingto an embodiment of the present invention will now be described withreference to FIGS. 2 and 3.

As shown in FIGS. 2 and 3, the electrophoretic display device accordingto an embodiment of the present invention includes: a first substrate101 having a plurality of pixels formed in a plurality of vertical pixelrows and a plurality of horizontal pixel rows; a plurality of data lines103 formed at every vertical pixel row of the first substrate 101; athin film transistor (TFT) 105 formed at each pixel of the firstsubstrate 101 and including a source electrode 105 a, a drain electrode105 b, an organic semiconductor layer 105 c, and a gate electrode 105 e;a passivation layer 108 formed on the TFTs 105 and the data lines 103 ofthe first substrate 101 and including a first contact hole 106 exposingthe drain electrode 105 b of the TFT 105 and a second contact hole 107exposing the gate electrode 105 e of the TFT 105; a pixel electrode 109formed on the passivation layer 108 at each pixel of the first substrate101 and connected with the drain electrode 105 b of the TFT 105 via thefirst contact hole 106 of the passivation layer 108; a plurality of gatelines 104 formed on the passivation layer 108 at every horizontal pixelrow of the first substrate 101 and connected with the gate electrode 105e of the TFT 105 via the second contact hole 107 of the passivationlayer 108; a second substrate 102 attached to the first substrate 101 ina facing manner; a common electrode 110 formed on the second substrate102; and an electrophoretic film (not shown) formed between the firstand second substrates 101 and 102.

The elements of the electrophoretic display device according to anembodiment of the present invention will now be described in detail.

The electrophoretic display device according to an embodiment of thepresent invention includes an electrophoretic panel including a firstsubstrate 101, an upper substrate, and a second substrate 102, a lowersubstrate, and an electrophoretic film (not shown) is formed between thefirst and second substrates 102.

Although not shown, the electrophoretic film includes a plurality ofcapsules including electronic ink of white and black ink distributedtherein, and the white ink and the black ink are charged with mutuallydifferent polarities. Namely, the white ink is charged with positivecharges and the black ink is charged with negative charges, or viceversa.

With reference to FIG. 2, a plurality of pixels are defined on the firstsubstrate 101, and the plurality of pixels form a plurality of verticalpixel rows and a plurality of horizontal pixel rows.

On the first substrate 101, a data line 103 is formed at every verticalpixel row, and a gate line 104 is formed at every horizontal pixel row.A thin film transistor (TFT) 105 is formed at each crossing of the gateline 103 and the data line 104.

With reference to FIGS. 2 and 3, the TFT 105 includes a source electrode105 a and a drain electrode 105 b formed on the first substrate 101, anorganic semiconductor layer 105 c formed on the source electrode 105 aand the drain electrode 105 b, a gate insulating layer 105 d formed onthe organic semiconductor layer 105 c, and a gate electrode 105 e on thegate insulating layer 105 d. The organic semiconductor layer 105 c, thegate insulating layer 105 d, and the gate electrode 105 e of the TFT 105are formed to have the same area and have the same overlap area. Namely,the organic semiconductor layer 105 c, the gate insulating layer 105 d,and the gate electrode 105 e of the TFT 105 are formed through a singlemasking process, details of which will be described in explaining amethod for fabricating the electrophoretic display device.

The gate electrode 105 e of the TFT 105 is connected to the gate line104, the source electrode 105 e is connected to the data line 103, andthe drain electrode 105 b is connected to the pixel electrode 109.

The organic semiconductor layer 105 c of the TFT 105 is made ofpentacene or polythiopene.

With reference to FIG. 3, the passivation layer 108 is formed on thedata line 103 and the TFT 105 of the first substrate 101. A firstcontact hole 106 exposing the drain electrode 105 b of the TFT 105 isformed at the passivation layer 108, and a second contact hole 107exposing the gate electrode 105 e of the TFT 105 is formed at thepassivation layer 108.

With reference to FIG. 3, the pixel electrode 109 is formed at eachpixel on the passivation layer 108. The pixel electrode 109 is connectedto the drain electrode 105 b of the TFT 105 in a corresponding pixel viathe first contact hole 106 of the passivation layer 108.

The gate line 104 is also formed on the passivation layer 108. The gateline 104 is connected to the gate electrode 105 e of the TFT 105 via thesecond contact hole 107, and made of the same material on the same layeras the pixel electrode 109.

The gate line 104 and the pixel electrode 109 are made of a transparentconductive material such as indium tin oxide (ITO) or an opaque metalsuch as molybdenum (Mo), aluminum (Al), chromium (Cr), copper (Cu), andthe like.

With reference to FIGS. 2 and 3, two second contact holes 107 are formedat each pixel on the passivation layer 108, and each gate line 104 isseparately formed at a plurality of regions. The plurality of regionsforming the gate line 104 are electrically connected via the secondcontact hole 107 and the gate electrode 105 e of the TFT 105. Namely,the gate line 104 is patterned to form the plurality of regions, butthey are electrically connected via the second contact hole 107 and thegate electrode 105 e of the TFT 105.

In FIGS. 2 and 3, two second contact holes 107 are shown to be formed,but the present invention is not limited thereto and three or moresecond contact holes 107 may be formed as necessary within the scope ofthe present invention.

Also, in FIGS. 2 and 3, the gate lines 104 are separately formed at aplurality of regions and the plurality of regions constituting the gatelines 104 are electrically connected to each other via the secondcontact hole 107 and the gate electrode 105 e of the TFT 105, but thepresent invention is not limited thereto and one gate line 104 may beformed without being separated into the plurality of regions and onesecond contact hole 107 may be formed within the scope of the presentinvention.

With reference to FIG. 3, the common electrode 110 is formed on thesecond substrate 102, and a common voltage is supplied to the commonelectrode 110.

When white ink in the capsules forming the electrophoretic film (notshown) formed between the first and second substrates 101 and 102 ischarged with positive charges and black ink is charged with negativecharges, a pixel voltage of a negative potential is applied to the pixelelectrode 109 and a common voltage of a positive potential is applied tothe common electrode 110. Then, the white ink of positive charges movestoward the pixel electrode 109 and the black ink of negative chargesmoves toward the common electrode 110 to implement black. Meanwhile,when the pixel voltage of positive potential is applied to the pixelelectrode 109 and the common voltage of negative potential is applied tothe common electrode 110, the white ink of positive charges moves towardthe common electrode 110 and the black ink of negative charges movestoward the pixel electrode 109, implement white. The plurality of pixelsare driven according to this principle, and as a result, an image isdisplayed on the electrophoretic panel.

The method for fabricating the electrophoretic display device accordingto an embodiment of the present invention will now be described withreference to FIGS. 4 a to 4 l.

First, the first substrate 101 on which a plurality of pixels aredefined and form the plurality of horizontal pixel rows and theplurality of vertical pixel rows is prepared.

Next, as shown in FIG. 4 a, a source/drain formation material layer 121and a photosensitive film 131 are sequentially formed on the firstsubstrate 101, on which photolithography is performed by using a firstmask 141 including a blocking region and an exposing region to form afirst photosensitive film pattern 151 as shown in FIG. 4 b.

The first mask 141 includes the blocking region formed at the regioncorresponding to the source electrode 105 a, the drain electrode 105 b,and the data line 103 to be formed in a follow-up stage, and theexposing region formed at other regions than the blocking region. Here,the exposing region and the blocking region of the first mask 141 may beinterchanged according to a type of the first photosensitive film 131.

And then, the source/drain formation material layer 121 is selectivelyremoved by using the first photosensitive film pattern 151 to form thesource electrode 105 a, the drain electrode 105 b, and the data line 103as shown in FIG. 4 c, and then, the first photosensitive film pattern151 is removed.

Thereafter, as shown in FIG. 4 d, an organic semiconductor materiallayer 122, a gate insulating layer formation material layer 123, a gateformation material layer 124, and a second photosensitive film 132 aresequentially formed on the first substrate 101, on whichphotolithography is performed by using a second mask 142 including ablocking region and an exposing region to form a second photosensitivefilm pattern 152 as shown in FIG. 4 e. Here, the organic semiconductormaterial layer 122 may be made of pentacene or polythiopene.

The second mask 142 includes the blocking region formed at the regioncorresponding to the organic semiconductor layer 105 c, the gateinsulating layer 150 d, and the gate electrode 105 e to be formed in afollow-up stage, and the exposing region formed at other regions thanthe blocking region. Here, the exposing region and the blocking regionof the second mask 142 may be interchanged according to a type of thefirst photosensitive film 132.

As shown in FIG. 4 f, the gate formation material layer 124 isselectively removed by using the second photosensitive film pattern 152to form the gate electrode 105 e, the gate insulating layer formationmaterial layer 123 is selectively removed by using the secondphotosensitive film pattern 152 to form the gate insulating layer 105 d,and the organic semiconductor material layer 122 is selectively removedby using the second photosensitive film pattern 152 to form the organicsemiconductor layer 105 c, and then, the second photosensitive filmpattern 152 is removed. At this time, the organic semiconductor layer105 c, the source electrode 105 a and the drain electrode 105 b areformed such that certain areas of them overlap with each other. Theorganic semiconductor layer 105 c, the gate insulating layer 105 d andthe gate electrode 105 e are formed to have the same area and have thesame overlap area.

As shown in FIG. 4 g, the passivation layer 108 and a thirdphotosensitive film 133 are sequentially formed on the first substrate101, on which photolithography is performed by using a third mask 143including a blocking region and an exposing region to form a thirdphotosensitive film pattern 153 as shown in FIG. 4 h.

The third mask 143 includes the blocking region formed at the regioncorresponding to the first contact hole 106 and the second contact hole107 to be formed in a follow-up stage, and the exposing region formed atother regions than the blocking region. Here, the exposing region andthe blocking region of the third mask 143 may be interchanged accordingto a type of the third photosensitive film 133.

And then, as shown in FIG. 4 i, the passivation layer 108 is selectivelyremoved by using the third photosensitive film pattern 153 to form thefirst and second contact holes 106 and 107, and then, the thirdphotosensitive film pattern 153 is removed.

Thereafter, as shown in FIG. 4 j, a conductive material layer 125 and afourth photosensitive film 134 are sequentially formed on the firstsubstrate 101, on which photolithography is performed by using a fourthmask including a blocking region and an exposing region to form a fourthphotosensitive film pattern as shown in FIG. 4 k. The conductivematerial layer 125 may be made of a transparent conductive material oran opaque metal. An example of the transparent conductive material maybe ITO, and an example of the opaque metal may be molybdenum (Mo),aluminum (Al), chromium (Cr), copper (Cu), and the like.

The fourth mask 144 includes the blocking region formed at the regioncorresponding to the pixel electrode 109 and the gate line 104 to beformed in a follow-up stage, and the exposing region formed at otherregions than the blocking region. Here, the exposing region and theblocking region of the fourth mask 144 may be interchanged according toa type of the fourth photosensitive film 134.

And then, the conductive material layer 125 is selectively removed byusing the fourth photosensitive film pattern 154 to form the pixelelectrode 109 and the gate line 104 as shown in FIG. 41, and then, thefourth photosensitive film pattern 154 is removed.

Thereafter, the second substrate (102 in FIG. 3) with the commonelectrode (110 in FIG. 3) is prepared, and the electrophoretic film (notshown) is formed between the first and second substrates 101 and 102.

The electrophoretic display device according to the embodiments of thepresent invention as described above is advantageous in terms of costsand time because the number of masks sued for the fabrication process isminimized. In addition, in the electrophoretic display device, becausethe pixel electrode 109 is formed on the passivation layer 108, so closeto the electrophoretic film, there is no need to form an open portion toexpose the pixel electrode 109.

As for the electrophoretic display device according to the embodimentsof the present invention, the first substrate 101 and the plurality ofelements formed on the first substrate 101 may be applicable to a TFTarray substrate of an LCD. In this case, because of the protection layer108 with the minimized step, rubbing can be smoothly performed on theentire region of an alignment layer and a problem such as liquid crystalis not fully charged and the like does not arise. Here, the alignmentlayer of the LCD is a means for initially aligning a liquid crystallayer formed between the TFT array substrate and a color filtersubstrate of the LCD.

As the present invention may be embodied in several forms withoutdeparting from the characteristics thereof, it should also be understoodthat the above-described embodiments are not limited by any of thedetails of the foregoing description, unless otherwise specified, butrather should be construed broadly within its scope as defined in theappended claims, and therefore all changes and modifications that fallwithin the metes and bounds of the claims, or equivalents of such metesand bounds are therefore intended to be embraced by the appended claims.

1. An electrophoretic display device comprising: a first substratehaving a plurality of pixels in a plurality of vertical pixel rows and aplurality of horizontal pixel rows; a plurality of data lines at everyvertical pixel row of the first substrate; a thin film transistor (TFT)at each pixel of the first substrate and including a source electrode, adrain electrode, an organic semiconductor layer, and a gate electrode; apassivation layer on the TFTs and the data lines of the first substrateand including a first contact hole exposing the drain electrode of theTFT and a second contact hole exposing the gate electrode of the TFT; apixel electrode on the passivation layer at each pixel of the firstsubstrate and connected with the drain electrode of the TFT via thefirst contact hole of the passivation layer; a plurality of gate lineson the passivation layer at every horizontal pixel row of the firstsubstrate and connected with the gate electrode of the TFT via thesecond contact hole of the passivation layer; a second substrateattached to the first substrate in a facing manner; a common electrodeformed on the second substrate; and an electrophoretic film between thefirst and second substrates.
 2. The device of claim 1, wherein theorganic semiconductor layer comprises one of pentacene or polythiopene.3. The device of claim 1, wherein the TFT comprises source and drainelectrodes on the first substrate, an organic semiconductor layer on thesource and drain electrodes, a gate insulating layer on the organicsemiconductor layer, and a gate electrode on the gate insulating layer,and the organic semiconductor layer, the gate insulating layer, and thegate electrode of the TFT have the same area and have the same overlaparea.
 4. The device of claim 1, wherein two or more second contact holesare formed at each pixel, each gate line is separately formed into aplurality of regions, and the separated regions are electricallyconnected via the second contact hole and the gate electrode of the TFT.5. The device of claim 1, wherein the pixel electrode and the gate lineare made of the same material on the same layer.
 6. The device of claim1, wherein the pixel electrode and the gate line are made of a materialselected from one of a transparent conductive material and an opaquemetal.
 7. The device of claim 1, wherein the pixel electrode and thegate line are made of a material selected from one of indium tin oxide(ITO), molybdenum (Mo), aluminum (Al), chromium (Cr), and copper (Cu).